• Title/Summary/Keyword: Cutoff Diameter

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Design and Performance Evaluation of a Low Pressure Impactor for Sampling Submicron Aerosols (서브마이크론 입자 측정용 저압 임팩터의 설계 및 성능평가)

  • Ji, Jun-Ho;Cho, Myung-Hoon;Bae, Gwi-Nam;Hwang, Jung-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.3
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    • pp.349-358
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    • 2004
  • A low pressure impactor is an impaction device to separate airborne particles into aerodynamic size classes at low pressure condition. We designed a two-stage low-pressure impactor to classify submicron sized environmental aerosols. Performance evaluation was carried out for stages 1 and 2 by using an electrical method. Monodisperse liquid dioctyl sebacate (DOS) particles were generated using evaporation-condensation process followed by electrostatic classification using a DMA (differential mobility analyzer). The test particles were in the range of 0.08∼0.8$\mu\textrm{m}$. For the evaluation of the impactor we used two electrometers; one was connected to the impaction plate of the impactor and the other was to the Faraday cage used as a backup filter. The effect of polydispersity of test aerosols on the performance was investigated. The results showed that the experimental 50-% cutoff diameters at each impactor's operation pressure were 0.53 and 0.187$\mu\textrm{m}$ for stages 1 and stage 2, respectively. The effects of operation pressure on the cutoff diameter and the steepness of collection efficiency curves were also investigated.

Design and Performance Evaluation of a Three Stage Impactor (대기 에어로졸 측정용 3단 임팩터의 설계 및 성능평가)

  • 지준호;배귀남;황정호
    • Journal of Korean Society for Atmospheric Environment
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    • v.17 no.6
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    • pp.441-450
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    • 2001
  • A three stage impactor with the cutoff diameters of 1, 2.5, and 10$\mu\textrm{m}$ in aerodynamic diameter was developed and tested. The gravimetric method and the particle counting method were utilized to evaluate the collection performance of each stage. A vibrating orifice aerosol generator was employed to generate monodisperse test aerosols larger that 2$\mu\textrm{m}$ in diameter. Polystyrene latex (PSL) particles smaller than 2$\mu\textrm{m}$ in diameter were generated by an atomizer and the particle number concentration was measured by an Aerodynamic Particle Sizer Spectrometer. The experimental cutoff diameters obtained from the particle collection efficiency curves are in good agreement with the designed values. The square roots of Stokes number at 50% collection efficiency for stage 1, 2, and 3 are 0.42, 0.48, and 0.45, respectively. Effects of the particle bounce and the impaction plate on the collection efficiency were investigated. The collection efficiency curves including effect of the particle bounce were also compared with those of the MOUDI cascade impactor.

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A Design Optimization on Coupling Joint between Exhaust Chimney of Electricity Generator and Electromagnetic Pulse (EMP) Shield (EMP 차폐를 위한 비상발전기 연도의 최적 형상 결정)

  • Pang, Seung-Ki;Kim, Jae-Hun
    • Journal of Energy Engineering
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    • v.24 no.4
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    • pp.159-165
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    • 2015
  • The article presents a parametric study on geometrical design optimization for coupling the joint between a large exhaust air chimney and electromagnetic pulse (EMP) shield for gas turbine electricity generator. We conducted computational fluid dynamics (CFD) simulations on hydraulic diameters of waveguide below cutoff(WBC) ranges 800mm~1025mm, the connection distance ranges 150~450mm, and exhaust gas flow velocities at 15, 20, and 25m/s. The results show that the diameter of main chimney, connection distance, and exhaust gas velocity had impacts on flow stream at the EMP shield. To provide a fully developed stream line at three different flow velocity cases, the WBC diameter and distance of connection should be larger than 1050mm and longer than 300mm, respectively.

Experimental panoramic positioning errors for inducing condylar cutoff and superimposition of cervical vertebrae on the mandibular ramus (하악과두 잘림과 경추의 하악지 겹침을 야기하는 파노라마방사선촬영 오류)

  • Kang, Byung Cheol;Kim, Min Jong;Park, Hye Sun;Hwang, Sel Ae;Yoon, Suk Ja;Lee, Jae Seo
    • The Journal of the Korean dental association
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    • v.56 no.3
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    • pp.134-141
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    • 2018
  • Purpose: To measure the head tilting angle creating initial condylar cut-off and to find the head position inducing the superimposition of the cervical vertebrae over the mandibular ramus on panoramic radiograph. Materials and Methods: The panoramic radiographs were taken with Didactic skull on cervical spine model (Scientific GmbH, Hamburg, Germany) using Kodak 8000c Digital Panoramic radiography. For the inherent radiolucency of the plastic skull model, radiopaque 1 mm diameter lead wires were attached along the margin of the mandibular condyle, ramus, mandibular body, cervical vertebrae, and FH plane of the skull model. For measuring the head tilting angle creating the condylar head cutoff, panoramic radiographs were taken by tilting the FH plane downward in 5 degree increments. For finding the distance between transverse process of the third cervical vertebra and gonion inducing superimposition of cervical vertebrae on the mandibular ramus, panoramic radiographs were taken by decreasing the distance in 0.5 cm increments. Result and Conclusion: The condylar cutoff began to appear when the head of skull model was tilted downward by 15o. As the head tilting angle increasing, the condylar cutoff became more prominent. The superimposition of cervical vertebrae over the mandibular ramus began to appear when the distance between the gonion and third cervical vertebra was 1.0 cm. As the distance decreasing, the superimpostion became more prominent.

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Transit Time Flowmetry and Vein Size Are Predictive of Arteriovenous Fistula Maturation

  • Kwon, Yelee;Cho, Young Jong;Kang, Pil Je;Cho, Won Chul
    • Journal of Chest Surgery
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    • v.53 no.5
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    • pp.297-300
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    • 2020
  • Background: This study aimed to assess the effect of vessel size and flow characteristics on the maturation of autogenous radiocephalic arteriovenous fistulae (RCAVFs). Methods: We retrospectively reviewed records of patients undergoing RCAVF creation at a single medical center from January 2013 to December 2019. Operative variables were compared between patients whose fistulae matured and those whose fistulae failed to mature. Results: Overall, 152 patients (33 of whom were women) with a mean age of 62.6±13.6 years underwent RCAVF creation; functional maturation was achieved in 123. No statistically significant differences were observed between patients in whom maturation was or was not achieved in terms of the following variables: female sex (20.3% vs. 25.0%), radial artery size (2.5 vs. 2.4 mm), and pulsatility index (0.69 vs. 0.62). Low intraoperative transit time flowmetry (TTF; 150.4 vs. 98.1 mL/min) and small vein size (2.4 vs. 2.0 mm) were associated with failure of maturation. The best cutoff diameter for RCAVF TTF and cephalic vein size were 105 mL/min and 2.45 mm, respectively. Conclusion: In patients who undergo RCAVF creation, vein diameter on preoperative ultrasonography and intraoperative TTF are predictors of functional maturation. We identified an intraoperative TTF cutoff value that can be used for intraoperative decision-making.

Electromagnetic Pulse (EMP) Shielding Effectiveness of Waveguide-Below-Cutoff (WBC) Arrays Installed in Generator Exhaust Chimney and its Effects on Gas Velocity (도파관 배열이 설치된 비상발전기 연도의 유속 예측 및 EMP 차폐평가)

  • Pang, Seung-Ki;Kim, Jae-Hun;Yook, Jong-Gwan;Kim, Yuna;Kim, Sangin;Kim, Suk-Bong
    • Journal of the Korean Society for Geothermal and Hydrothermal Energy
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    • v.12 no.1
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    • pp.1-6
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    • 2016
  • Characteristics of exhaust from chimney of electricity generator are analyzed based on CFD when Waveguide-Below-Cutoff (WBC) array is installed in order to achieve the certain level of electromagnetic pulse (EMP) shielding. The main purpose is prediction of average and maximum velocity of exhaust. The results reveal that: 1) When the specification of waveguide is given as 80-diameter, 400-length, and the gap of 20 mm, the shielding effectiveness (SE) is 140dB. The average and maximum velocity of exhaust in the chimney with WBC Array can be represented as exponential functions. 2) As the number of WBC increases, the velocity in the chimney dwindles. 3) Under the situation that WBC with 80 mm diameter is located at intervals of 20 mm, the average velocity can be approximated by $25.5344{\times}e^{(-0.0098{\times}N_{WBC})}$ with input velocity of 15 m/s. In addition, the determination coefficient is 0.915, which is sufficiently high.

Feasibility and reliability of various morphologic features on magnetic resonance imaging for iliotibial band friction syndrome

  • Jin Kyem Kim;Taeho Kim;Hong Seon Lee;Dong Kyu Kim
    • The Korean Journal of Pain
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    • v.36 no.2
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    • pp.208-215
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    • 2023
  • Background: To evaluate the feasibility, inter-reader reliability, and intra-reader reliability for various morphological features reported to be related to iliotibial band friction syndrome (ITBFS) on knee magnetic resonance imaging (MRI). Methods: A total of 145 patients with a clinical diagnosis and knee MRI findings consistent with ITBFS were included in the "study group" and 232 patients without knee pathology on both physical examination and MRI were included in the "control group". Various morphologic features on knee MRI were assessed including the patella shape, patella height, lateral epicondyle anterior-posterior (AP) width, lateral epicondyle height, ITB diameter (ITB-d), and ITB area (ITB-a). Results: Patients in the study group had significantly higher lateral epicondyle height (13.9 mm vs. 12.92 mm, P = 0.003), ITB-d (2.9 mm vs. 2.0 mm, P = 0.022), and ITB-a (38.5 mm2 vs. 23.8 mm2, P < 0.001) than the control group. ITB-a showed higher area under the curve index (0.849 with 74.1% sensitivity and 72.4% specificity at a 30.3 mm2 cutoff) than ITB-d (0.710 with 70.8% sensitivity and 61.2% specificity at 2.4 mm cutoff) and lateral epicondyle height (0.776 with 72.4% sensitivity and 67.8% specificity at 13.4 mm cutoff). However, only the inter-reader agreement for ITB-a (intraclass correlation coefficient = 0.65) was moderate, while the agreements for other morphologic features were good or excellent. Conclusions: Lateral epicondyle height seems to be a reliable and feasible morphologic feature for diagnosis of ITBFS.

Design of a 94-GHz Single Balanced Mixer Using Planar Schottky Diodes with a Nano-Dot Structure on a GaAs Substrate

  • Uhm, Won-Young;Ryu, Keun-Kwan;Kim, Sung-Chan
    • Journal of information and communication convergence engineering
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    • v.14 no.1
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    • pp.35-39
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    • 2016
  • In this paper, we develop a 94-GHz single balanced mixer with low conversion loss using planar Schottky diodes on a GaAs substrate. The GaAs Schottky diode has a nanoscale anode with a T-shaped disk that can yield high cutoff frequency characteristics. The fabricated Schottky diode with an anode diameter of 500 nm has a series resistance of 21 Ω, an ideality factor of 1.32, a junction capacitance of 8.03 fF, and a cutoff frequency of 944 GHz. Based on this technology, a 94-GHz single balanced mixer was constructed. The fabricated mixer shows an average conversion loss of -7.58 dB at an RF frequency of 92.5 GHz to 95 GHz and an IF frequency of 500 MHz with an LO power of 7 dBm. The RF-to-LO isolation characteristics were greater than -32 dB. These values are considered to be attributed to superior Schottky diode characteristics.

Design and Performance Evaluation of Electrical Impactor for Nano Environmental Aerosols (나노 환경입자 측정용 전기적 임팩터의 설계 및 성능평가)

  • Ji, Jun-Ho;Cho, Myung-Hoon;Bae, Gwi-Nam;Hwang, Jung-Ho
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1417-1422
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    • 2003
  • An electrical cascade impactor is a multistage impaction device to separate airborne particles into aerodynamic size classes using electrical method. We designed a real-time three-stage electrical low-pressure impactor, which is proper to nanometer sized environmental aerosols. Performance evaluation was carried out for stage 1 and 2. The monodisperse liquid dioctyl sebacate (DOS) particles were generated using condensation-evaporation followed by electrostatic classification using DMA (differential mobility analizer) for particles with diameters in the range of $0.04{\sim}0.8{\mu}m$. The evaluation of the electrical impactor is based on the use of two electrometers, one connected to the impaction plate of the impactor, and the other to the faraday cage as backup filter. The results showed that the experimental 50% cutoff diameters in the operation pressure were 0.53 and $0.12{\mu}m$ for stage 1 and stage 2. The effect of operation pressure on the cutoff diameter and the steepness of collection effcieicy curves is investigated.

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Improvement of a High-volume Aerosol Particle Sampler for Collecting Submicron Particles through the Combined Use of a Cyclone with a Smoothened Inner Wall and a Circular Cone Attachment

  • Okuda, Tomoaki;Isobe, Ryoma
    • Asian Journal of Atmospheric Environment
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    • v.11 no.2
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    • pp.131-137
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    • 2017
  • A cyclone is an effective tool to facilitate the collection of aerosol particles without using filters, and in cell exposure studies is able to collect a sufficient amount of aerosol particles to evaluate their adverse health effect. In this study, we examined two different methods to improve the aerosol particle collection efficiency of a cyclone. The individual and combined effects of reducing the surface roughness of the inner wall of the cyclone and of using a circular cone attachment were tested. The collection efficiency of particles of diameter $0.2{\mu}m$ was improved by approximately 10% when using a cyclone with a smoothened inner wall (average roughness $Ra=0.08{\mu}m$) compared with the original cyclone ($Ra=5.1{\mu}m$). A circular cone attachment placed between the bottom section of the cyclone and the top section of a collection bottle, resulted in improved collection of smaller particles without the attachment. The 50% cutoff diameter of the modified cyclone (combined use of smoothened inner wall and attachment) was $0.23{\mu}m$ compared to $0.28{\mu}m$ in the original model. The combined use of these two techniques resulted in improved collection efficiency of aerosol particles.